a) Field of the Invention
The present invention relates to a control apparatus for a continuously variable transmission, and more particularly, to an apparatus for controlling the gear ratio of the continuously variable transmission by use of a flow control unit.
b) Description on the Related Art
Continuously variable transmissions have hitherto been used as transmissions for automobiles and so on. With a belt type continuously variable transmission, a V belt is passed around the primary pulley on the engine side and the secondary pulley on the wheel side, thus continuously changing the gear ratio by changing the groove widths of the primary and secondary pulleys.
Driving force required to change the gear ratio of this transmission is generally produced by hydraulic pressure from a hydraulic actuator. The flow control unit as shown, for example, in Japanese Patent Laid-open publication No. Hei11-182667 is employed as a hydraulic actuator. The flow control unit shown in Japanese Patent Laid-open publication No. Hei11-182667 comprises a shift-up flow control valve and a shift-down flow control valve which are separate from each other and further comprises shift-up and shift-down solenoid valves designed respectively to control the shift-up and shift-down flow control valves.
During shift up, duty control is performed in which the shift up shift-up flow control valve is turned on and off repeatedly, thus allowing operating fluid to flow from the shift-up flow control valve to the primary pulley""s fluid chamber. This causes the turning radius of the portion of the primary pulley around which the V belt is passed to increase, thus allowing shift up. During shift down, on the other hand, duty control is performed in which the shift-down flow control valve is turned on and off repeatedly, thus allowing operating fluid to flow from the shift-down flow control valve through the primary pulley""s fluid chamber. This causes the turning radius of the portion of the primary pulley around which the V belt is passed to decrease, thus allowing shift down. Here, the orifice area within the flow control valves is determined based on the duty ratio of the solenoid valves. A characteristic of the duty ratio with respect to the orifice area is stored in advance in an electronic control unit, and the duty ratio of the solenoid valves is calculated based on this characteristic.
Since manufacturing variation occurs in flow control and solenoid valves, variation also occurs in that characteristic of the duty ratio with respect to the orifice area. Consequently, the characteristic of the duty ratio with respect to the orifice area stored in the electronic control unit does not necessarily agree with the actual characteristic of the flow control unit for the duty ratio with respect to the orifice area, thus resulting in difference in characteristic between the two. Consequently, an error occurs between the desired and actual flow rates, thus aggravating the ability of actual gear ratio to follow desired gear ratio.
Additionally, a continuously variable transmission achieves change gear control by determining target input rotation speed based, for example, on required amount of driving force such as an accelerator opening amount and driving conditions such as vehicle speed or operation by the driver and by controlling gear ratio such that actual input rotation speed agrees with target input rotation speed. A change gear control device which controls the gear ratio of a continuously variable transmission such that actual input rotation speed agrees with target input rotation speed is included in Japanese Patent Laid-Open Publication No. Hei 7-4508. With this conventional technology, feedforward and feedback manipulated variables are added, a control value appropriate for manipulated variable is treated as a shift actuator manipulated variable, a feedback manipulated variable which provides a near-zero deviation of actual input rotation speed from target speed is stored as a correction manipulated variable and this correction manipulated variable is added to feedforward and feedback manipulated variables. This allows learning and correction of changes in feedforward characteristic caused by individual differences between continuously variable transmissions and deterioration over time.
With conventional continuously variable transmissions, however, there has been a problem of shift characteristic aggravation as a result of variation in control value if the feedforward manipulated variable is reflected in an actuator manipulated variable before learning of actuator manipulated variable is complete.
The present invention was conceived in view of the above problems, and an advantage of the present invention is that it provides a control apparatus for a continuously variable transmission which improves the ability of the actual gear ratio to follow a desired gear ratio.
Another advantage of the present invention is that it provides a control apparatus for a continuously variable transmission which ensures reduced variation in change gear control value before learning of actuator manipulated variable is complete.
In order to achieve the advantages, according to a first aspect of the present invention there is provided a control apparatus for a continuously variable transmission which controls the gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid entering and leaving a gear change mechanism, the control apparatus comprising a hydraulic control signal calculation device which calculates a hydraulic control signal output to the operating fluid supply and discharge device, a fluid volume detection device which detects a change in operating fluid volume within the gear change mechanism over a predetermined period of time during which a gear change operation is in progress, a fluid volume estimation device which estimates a change in operating fluid volume within the gear change mechanism over the predetermined period of time, based on the hydraulic control signal, and a correction device which corrects the hydraulic control signal to flow control output characteristic map, based on the deviation of the value detected by the fluid volume detection device from the value estimated by the fluid volume estimation device.
According to the present invention, since the hydraulic control signal to flow control output characteristic map for the operating fluid supply and discharge device is corrected based on the deviation of the value detected by the fluid volume detection device from the value estimated by the fluid volume estimation device, it is possible to accurately learn and correct any difference between the characteristic map stored in the electronic control unit and the actual characteristic of the operating fluid supply and discharge device. Consequently, error between desired and actual flow rates can be minimized, thus providing improved ability of actual gear ratio to follow desired gear ratio.
In the present invention, the fluid volume estimation device may include a differential pressure detection device which detects the difference between operating fluid pressures anterior and posterior to the operating fluid supply and discharge device, the fluid volume estimation device estimating a change in operating fluid volume within the gear change mechanism, based on the hydraulic control signal and on the value detected by the differential pressure detection device. The fluid volume estimation device may estimate a change in operating fluid volume within the gear change mechanism, based on the hydraulic control signal, on the value detected by the differential pressure detection device and on a dynamic characteristic model for the hydraulic control signal with respect to the flow control output.
By estimating change in operating fluid volume within the gear change mechanism based on the dynamic characteristic model for the hydraulic control signal and the flow control output, it is possible to consider response delay of the operating fluid supply and discharge device and more accurately estimate change in operating fluid volume within the gear change mechanism. Consequently, the hydraulic control signal to flow control output characteristic map can be learned and corrected more accurately.
In the present invention, the correction device may correct the hydraulic control signal to flow control output characteristic map for the range of hydraulic control signal values used for estimation of a change in operating fluid volume by the fluid volume estimation device.
By correcting the hydraulic control signal to flow control output characteristic map for the range of hydraulic control signal values used for estimation of change in operating fluid flow rate, it is possible to perform accurate learning and correction even if the difference between the characteristic map stored in the electronic control unit and the actual characteristic of the operating fluid supply and discharge device changes in accordance with the hydraulic control signal.
In the present invention, the gear change mechanism may comprise a primary pulley to which driving torque is transferred from a prime mover, a secondary pulley which transfers driving torque to a load and a belt which is passed around the primary pulley and the secondary pulley, wherein the operating fluid supply and discharge device controls the gear ratio by changing the flow rate of operating fluid entering and leaving the primary pulley, wherein the control apparatus further includes a primary rotation speed detection device which detects the primary pulley rotation speed, a secondary rotation speed detection device which detects the secondary pulley rotation speed, an input torque detection device which detects input torque transferred to the primary pulley and a secondary pressure detection device which detects operating fluid pressure within the secondary pulley and wherein the differential pressure detection device detects the difference between operating fluid pressures anterior and posterior to the operating fluid supply and discharge device, based on the values detected by the primary rotation speed detection device, the secondary rotation speed detection device, the input torque detection device and the secondary pressure detection device.
By detecting the difference between operating fluid pressures anterior and posterior to the operating fluid supply and discharge device based on the primary pulley rotation speed, the secondary pulley rotation speed, input torque transferred to the primary pulley and operating fluid pressure within the secondary pulley, it is possible to do without the pressure sensor for detecting operating fluid pressure within the primary pulley, thus reducing costs.
In the present invention, the control apparatus may further comprise a gear ratio detection device which detects the gear ratio of the continuously variable transmission, wherein the fluid volume detection device detects a change in operating fluid volume within the gear change mechanism, based on the amount of change in the gear ratio over the predetermined period of time.
In the present invention, the predetermined period of time is preferably from the start of a gear change operation to the end of gear change operation.
In the present invention, the flow control output is preferably the orifice area of the operating fluid supply and discharge device.
In the present invention, the control apparatus may further comprise a gear ratio detection device which detects the gear ratio of the continuously variable transmission, wherein the fluid volume estimation device stops estimating a change in operating fluid volume within the gear change mechanism if the gear ratio falls outside a preset range. If gear ratio falls outside the set range, estimation of change in operating fluid volume within the gear change mechanism is stopped, thus preventing erroneous learning caused by gear ratio reaching the maximum or minimum ratio during learning and correction of the hydraulic control signal to flow control output characteristic map stored in the electronic control unit and ensuring more accurate learning and correction.
According to a second aspect of the present invention there is provided a control apparatus for a continuously variable transmission which controls gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid entering and leaving a gear change mechanism, the control apparatus comprising a hydraulic control signal calculation device which calculates a hydraulic control signal output to the operating fluid supply and discharge device, a fluid flow detection device which detects the flow rate of operating fluid entering and leaving the gear change mechanism at a predetermined timing during the gear change operation, a fluid flow estimation device which estimates the flow rate of operating fluid entering and leaving the gear change mechanism at the predetermined timing based on the hydraulic control signal, and a correction device which corrects a hydraulic control signal to flow control output characteristic map for the operating fluid supply and discharge device, based on the deviation of the value detected by the fluid flow detection device from the value estimated by the fluid flow estimation device. The correction device may further correct a hydraulic control signal value when flow begins to occur at the operating fluid supply and discharge device, based on the hydraulic control signal and the value detected by the fluid flow detection device. By correcting the hydraulic control signal value when flow begins to occur at the operating fluid supply and discharge device based on the hydraulic control signal and the value detected by the fluid flow detection device, it is possible to accurately learn and correct the hydraulic control signal value when flow begins to occur at the operating fluid supply and discharge device. Consequently, it is possible to perform accurate gear ratio control using the operating fluid supply and discharge device when gear ratio is changed only slightly, thus minimizing gear ratio hunting in which shift up and shift down are repeated to maintain gear ratio at a desired level.
In the present invention, the correction device may correct a hydraulic control signal value when flow begins to occur at the operating fluid supply and discharge device, based on the hydraulic control signal, the value detected by the fluid flow detection device and a dynamic characteristic model for the hydraulic control signal with respect to the flow control output. By correcting the hydraulic control signal value when flow begins to occur at the operating fluid supply and discharge device based on the dynamic characteristic model for the hydraulic control signal with respect to the flow control output, it is possible to consider response delay of the operating fluid supply and discharge device and more accurately learn and correct the hydraulic control signal value when flow begins to occur at the operating fluid supply and discharge device. Consequently, gear ratio hunting can be further minimized.
In the present invention, the fluid flow estimation device may include a differential pressure detection device detecting the difference between operating fluid pressures anterior and posterior to the operating fluid supply and discharge device, the fluid flow estimation device estimating the flow rate of operating fluid entering and leaving the gear change mechanism, based on the hydraulic control signal and the value detected by the differential pressure detection device. The fluid flow estimation device may estimate the flow rate of operating fluid entering and leaving the gear change mechanism, based on the hydraulic control signal, the value detected by the differential pressure detection device and a dynamic characteristic model for the hydraulic control signal with respect to the flow control output.
In the present invention, the correction device may correct the hydraulic control signal to flow control output characteristic map for the hydraulic control signal value used for estimation of flow rate of operating fluid by the fluid flow estimation device.
In the present invention, the gear change mechanism may comprise a primary pulley to which driving torque is transferred from a prime mover, a secondary pulley which transfers driving torque to load and a belt which is passed around the primary pulley and the secondary pulley, wherein the operating fluid supply and discharge device controls gear ratio by changing the flow rate of operating fluid entering and leaving the primary pulley, wherein the control apparatus further has a primary rotation speed detection device which detects the primary pulley rotation speed, a secondary rotation speed detection device which detects the secondary pulley rotation speed, an input torque detection device which detects input torque transferred to the primary pulley and a secondary pressure detection device which detects operating fluid pressure within the secondary pulley and wherein the differential pressure detection device detects the difference between operating fluid pressures anterior and posterior to the operating fluid supply and discharge device, based on the values detected by the primary rotation speed detection device, the secondary rotation speed detection device, the input torque detection device and the secondary pressure detection device.
In the present invention, the control apparatus may further comprise a gear ratio detection device which detects the gear ratio of the continuously variable transmission, wherein the fluid flow detection device detects the flow rate of operating fluid entering and leaving the gear change mechanism, based on the amount of change in gear ratio per unit time at the predetermined timing.
In the present invention, the flow control output is preferably the orifice area of the operating fluid supply and discharge device.
In the present invention, the hydraulic control signal calculation device may include a feedforward control device which calculates a feedforward manipulated variable to be sent to the operating fluid supply and discharge device, based on the hydraulic control signal to flow control output characteristic map and wherein control by the feedforward control device is disabled until the correction device completes correction of the hydraulic control signal to flow control output characteristic map.
In the present invention, the hydraulic control signal calculation device may include a feedforward control device which calculates a feedforward manipulated variable to be sent to the operating fluid supply and discharge device based on the hydraulic control signal to flow control output characteristic map and a feedback control device which calculates a feedback manipulated variable to be sent to the operating fluid supply and discharge device and wherein control by the feedforward control device is disabled and control by the feedback control device is enabled until the correction device completes correction of the hydraulic control signal to flow control output characteristic map.
In the present invention, the hydraulic control signal calculation device may include a feedforward control device which calculates a feedforward manipulated variable to be sent to the operating fluid supply and discharge device based on the hydraulic control signal to flow control output characteristic map, a feedback control device which calculates a feedback manipulated variable to be sent to the operating fluid supply and discharge device and a weight setting device which specifies weights for feedforward and feedback manipulated variables and wherein the weight for a feedforward manipulated variable is increased in accordance with the progress of correction of the hydraulic control signal to flow control output characteristic map by the correction device.
In the present invention, control by the feedforward control device may be disabled under those operating conditions to which correction of the hydraulic control signal to flow control output characteristic map by the correction device is not applicable.
In the present invention, the control apparatus may further comprise a fluid temperature measurement device which measures operating fluid temperature, wherein control by the feedforward control device is disabled under those operating fluid temperatures to which correction of the hydraulic control signal to flow control output characteristic map by the correction device is not applicable.
In the present invention, the hydraulic control signal calculation device may include a feedback control device which calculates a feedback manipulated variable to be sent to the operating fluid supply and discharge device and wherein feedback gain for the feedback control device is changed in accordance with the progress of correction of the hydraulic control signal to flow control output characteristic map by the correction device.
In the present invention, a feedback gain for the feedback control device equal to or lower than a predetermined value may be specified under those operating conditions to which correction of the hydraulic control signal to flow control output characteristic map by the correction device is not applicable.
In the present invention, the control apparatus may further comprise a fluid temperature measurement device which measures operating fluid temperature, wherein a feedback gain for the feedback control device equal to or lower than a predetermined value is specified under those operating fluid temperatures to which correction of the hydraulic control signal to flow control output characteristic map by the correction device is not applicable.
According to a third aspect of the present invention there is provided a control apparatus for a continuously variable transmission which controls the gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid, the control apparatus comprising a feedforward control device which uses a physical model to calculate a feedforward manipulated variable to be sent to the operating fluid supply and discharge device, and a correction device which corrects the physical model from control results and repeats correction of the physical model, wherein control by the feedforward control device is disabled until correction of the physical model is complete.
According to a fourth aspect of the present invention there is provided a control apparatus for a continuously variable transmission which controls gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid, the control apparatus comprising a feedforward control device which uses a physical model to calculate a feedforward manipulated variable to be sent to the operating fluid supply and discharge device, a correction device which corrects the physical model from control results and repeats correction of the physical model, and a feedback control device which calculates a feedback manipulated variable to be sent to the operating fluid supply and discharge device, wherein control by the feedforward control device is disabled and control by the feedback control device is enabled until correction of the physical model is complete.
According to a fifth aspect of the present invention there is provided a control apparatus for a continuously variable transmission which controls gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid, the control apparatus comprising a feedforward control device which uses a physical model to calculate a feedforward manipulated variable to be sent to the operating fluid supply and discharge device, a correction device which corrects the physical model from control results and repeats correction of the physical model, a feedback control device which calculates a feedback manipulated variable to be sent to the operating fluid supply and discharge device, and a weight setting device which specifies weights for feedforward and feedback manipulated variables, wherein the weight for feedforward manipulated variable is increased in accordance with the progress of correction of the physical model.
In the present invention, control by the feedforward control device may be disabled under those operating conditions to which the physical model is not applicable.
In the present invention, the control apparatus may further comprise a fluid temperature measurement device which measures operating fluid temperature, wherein control by the feedforward control device is disabled under those operating fluid temperatures to which the physical model is not applicable.
According to a sixth aspect of the present invention, there is provided a control apparatus for a continuously variable transmission which controls gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid, the control apparatus comprising a feedback control device which uses a physical model to calculate a feedback manipulated variable to be sent to the operating fluid supply and discharge device, and a correction device which corrects the physical model from control results and repeats correction of the physical model; wherein a feedback gain for the feedback control device is changed in accordance with the progress of correction of the physical model.
In the present invention, a feedback gain for the feedback control device equal to or lower than a predetermined value may be specified under those operating conditions to which the physical model is not applicable.
In the present invention, the control apparatus may further comprise a fluid temperature measurement device which measures operating fluid temperature, wherein a feedback gain for the feedback control device equal to or lower than a predetermined value is specified under those operating fluid temperatures to which the physical model is not applicable.
In the present invention, preferably, the operating fluid supply and discharge device includes a flow control valve and solenoid valve, wherein a solenoid valve control value corresponding to the manipulated variable allows the solenoid valve to change the orifice area of the flow control valve, thus changing operating fluid flow rate, wherein the physical model is a model which brings the solenoid valve control value into correspondence with operating fluid flow rate and wherein the correction device corrects the physical model from the difference between actual operating fluid flow rate obtained through control results and flow rate of the physical model and repeats correction of the physical model.